The term supervisory control and data acquisition systems – also known as SCADA – is quite a mouthful. In reality SCADA is a well-established, if not complex, means for monitoring utilities (among other production and critical infrastructure applications) remotely. SCADA systems collect the data and automate it across the utility’s applications.
By definition, SCADA systems are industrial control systems (ICS). They fall into the operations technology (OT) classification, which describes the hardware, software, and communication technology used in creating, storing, exchanging, and using information.
No matter what they are monitoring, however, SCADA systems are essentially built the same. They pull together hardware, software, and connectivity and then organize it into four layers: field instrumentation; programmable logic controllers (PLCs) and remote telemetry units (RTUs); communications; and the SCADA host platform.
While typical applications for SCADA systems include manufacturing plants, oil & gas refineries, power plants, and water and wastewater treatment plants and remote utilities monitoring, this blog will focus exclusively on water/wastewater, energy and other utilities monitoring.
The first layer of a SCADA system consists of field instrumentation hardware. In a water utility, for instance, instrumentation systems are typically comprised of sensors, samplers, relays, and actuators. In this application, a temperature or pH sensor inserted into a drinking water pipe measures fluctuations over time, which can reflect changes in water quality. Piezo vibration sensors can measure physical stress on pumps and generators. An actuator powered by an electric source can convert that electric energy into mechanical energy to close a valve, for example. From the perspective of monitoring and automation, field instrumentation generates data, requires data, or both creates and consumes data.
PLCs and RTUs
SCADA systems’ second layer consists of PLCs and RTUs (note: remote telemetry unit and remote terminal unit are used interchangeably to refer to the same class of devices). PLCs and RTUs are connected to field instrumentation and perform real-time or continuous data collection. They then relay data to the SCADA host platform, and perform varying levels of control.
As the name suggests, PLCs are designed and engineered for industrial control and automation based on the programmable processing of measurements. These digital computers are hard-wired for real- or near-real-time processing and response at the installation point to ensure proper operations and avoid potentially disastrous mishaps. Typically, PLCs support many analog and digital inputs (such as sensors) and outputs (such as relays and actuators for pump, valve, and hydraulic cylinder operational control). PLCs and the microprocessors that power their computing capabilities are ruggedized to withstand harsh conditions, including dust, humidity, vibration, heat, and cold. Moreover, PLCs use more stable operating systems suitable for deterministic logic execution.
Those familiar with RTUs know they were once relatively crude telemetry devices that logged data from field instrumentation and relayed it over fixed or wireless communication networks to the SCADA host platform. Early RTUs lacked the processing and control capabilities of PLCs, but had more sophisticated communication capabilities. Without doubt, legacy RTUs are still deployed in the field and many utilities still rely on legacy technology with limited communication capabilities by today’s standards.
However, in the past few decades, the once highly differentiated technologies of PLCs and RTUs have blurred. Manufacturers of PLCs and RTUs alike have responded to evolving customer demands for improved communications capabilities from PLCs and more robust processing and control capabilities from RTUs. While PLCs and RTUs are increasingly analogous, there is still a meaningful divide on the control capabilities that is reflected in the higher cost of PLCs.
Through the third SCADA system layer – communications – PLCs and RTUs connect field instrumentation to the SCADA host platform. SCADA systems establish connectivity through wired or wireless (radio, satellite) networks using a variety of communication protocols.
Over the past few decades, the typical communication channel for SCADA systems has evolved to fiber optic cable.
SCADA systems were first developed for inside-of-the-fence applications such as factory floors, where power supply is readily available on-site and field instrumentation and the SCADA host platform are co-located or within close proximity. But they have evolved. They are now widely used for monitoring and industrial automation for outside-of-the-fence applications, such as water, wastewater, electric power, and natural gas utilities.
As the number of SCADA system developers and integrators has grown, vendors competing over lucrative procurement contracts have sought sources of differentiation (and the result is some market fragmentation). For example, there is a wide variety of communication protocols, which act as the glue connecting PLCs and RTUs with the SCADA host platform. The industry is slowly moving away from old and proprietary protocols to ones which are non-proprietary. OLE (object linking and embedding) for Process Control (OPC) and Distributed Network Protocol (DNP3) were developed by industry consortiums and first released in 1996 and 1993, respectively.
OPC establishes a standard set of objects, interfaces, and methods that govern communication of the SCADA host platforms with PLCs and RTUs. The legacy OPC protocol is based on OLE, COM (Component Object Model), and DCOM (Distributed Component Object Model) technologies developed for Microsoft Windows.
Distributed Network Protocol (DNP3), like OPC, was developed to achieve open, standards-based interoperability between various SCADA systems vendors’ components. Originally designed with the needs of electric utilities in mind, DNP3 enables more reliable communications in challenging conditions, including where distortion can be created by electromagnetic interference. In addition to electric power utilities, the DNP3 communication protocol has been adopted by water and wastewater utilities, oil & gas operators, and others.
SCADA Host Platform
For the software and information technology layer, SCADA host platforms include: software drivers; a SCADA engine; one or multiple databases; and a human machine interface (HMI). The host platform is effectively the nerve center of the SCADA system architecture.
SCADA host platforms operate as follows: data streams generated by field instrumentation flow in via PLCs and RTUs over the communication layer; communication drivers then integrate data with the engine; the engine stores and runs queries from a database architecture, provides graphical displays of field instrumentation and physical processes, visualizes data and trends, and alarms. The final aspect of the SCADA host platform is the HMI, which is the means by which SCADA engineers, operators, technicians, and other decision makers manage the entire SCADA system architecture and control strategy.
The SCADA host platform drives the lion’s share of value-add, which is derived from its feedback mechanisms. As a data fusion and analytics platform, the SCADA engine is responsible for integrating data from the field and subsequently delivering commands to PLCs, RTUs, and field instrumentation to automate and improve machinery and infrastructure management.
The digitalization of information and increasingly pervasive internet connectivity have changed many facets of everyday life. One of the most promising and discussed areas of current and future innovation is what technologists and analysts now often refer to as the Internet of Things (IoT), the Internet of Everything (IoE), and in the industrial sector as the Industrial Internet of Things (IIoT). In the industrial sector, especially where assets are dispersed and situated in remote locations, SCADA systems are the heart and brain that manage data collection, perform data fusion and analytics, and automate industrial processes.